Horizontal regenerative catalytic oxidizer

ABSTRACT

A system for the abatement of industrial process emissions comprises a horizontal regenerative catalytic oxidizer (RCO). The system utilizes at least two regenerative chambers and at least two catalytic chambers in a controlled abatement process. Pollutants injected into the RCO from the process emissions are catalytically oxidized. The horizontal configuration of the RCO reduces the size of the RCO per cubic foot of emissions treated, and also simplifies maintenance requirements in removing and replacing, or regenerating, the catalyst. Chutes and valves situated above and below the catalyst provide maintenance means without the associated contamination concerns typically caused by catalytic migration throughout vertically configured RCOs.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a divisional of copending U.S. patentapplication Ser. No. 08,742,807 file on Nov. 1, 1996.

BACKGROUND OF THE INVENTION

The present invention relates generally to the abatement of contaminantladen industrial process emissions and more particularly, to a systemwhich utilizes a regenerative catalytic oxidizer (RCO) to perform theabatement process.

Regenerative catalytic oxidizers recover and transfer heat remaining inthe cleansed exhaust gas to emissions entering the oxidizer therebyminimizing the amount of supplemental energy required to raise theemission to its ignition temperature. Characteristically, flow controlvalves are used to direct the emissions to one or more regenerators forpreheating prior to thermal or catalytic oxidation.

Industrial process emissions typically contain particulates and majorgaseous air pollutants such as volatile organic compounds (VOCs),nitrogen oxides (NO_(x)) and carbon monoxide (CO), all of whichcontaminate the environment when vented to the atmosphere. Regenerativecatalytic oxidizers (RCO) utilize a catalytic material to effectoxidation of the VoCs and CO at lower peak temperatures than, forexample, treatment by thermal oxidation. The catalytic material islocated in the higher temperature zones of the RCO, adjacent to acombustion chamber wherein a burner or supplementary heat source is usedto heat the catalyst. An RCO also utilizes heat storage media, usuallylocated in the lower temperature zones at the gas entrance and exitports, thereby facilitating fluid heat transfer as the heated gas ispassed through.

The system typically consists of multiple beds of heat storage andcatalyst materials. These beds are connected to a common chamber where aheater, such as a burner, is utilized to heat the gas to the desiredoperating temperature, normally in the range of 600° F. (≈315° C.) to1000° F. (≈540° C.), thereby effecting catalytic conversion of the VOCs,and CO, and producing water and CO₂.

As the catalyst becomes aged due to repeated reaction of gases, theexhausted catalyst must either be regenerated or be replaced. Shape iscritical when considered in a maintenance context. If regenerativecleaning is a design consideration, random catalysts such as sphericalor saddle shaped catalytic particles are preferred. The commonlydesigned honeycomb configuration is not readily regenerated by water orother cleaning agents given the entrainment of these fluids due toblockages within the catalytic bed.

RCOs generally utilize a vertical orientation of components resulting invertical flow in and out of the reactor. Such vertical orientation isless than desirable for several reasons. Due to channeling andinefficient utility related to a vertical emission flow regime, avertically orientated RCO must be significantly sized per cubic foot ofprocess emissions treated. In addition, because the catalyst isgenerally disposed immediately above the heat media, percolation of thecatalytic material through the heat media can cause blockages andinefficient heat exchange within the heat exchange bed. Furthermore,again due to possible heat media contamination, the vertical designmakes catalyst regeneration, or removal and replacement, difficult.

SUMMARY OF THE INVENTION

The aforesaid problems are solved, in accordance with a preferredconstructed embodiment of the present invention, by an abatement systemfor industrial process emissions comprising a horizontal regenerativecatalytic oxidizer. The present invention provides for simplifiedremoval and replacement, or regeneration of catalytic material therebyreducing maintenance and operational expenses.

The present invention operates in abatement cycles and comprises aplurality of regenerative beds and a corresponding number of catalyticbeds that when positioned together form a single horizontal orientatedsystem. The emissions flow from a contaminated feed duct through aselectively opened valve and inlet duct to a regenerative chamber forpreheating. The emissions then flow through a catalytic oxidizer, whichoxidizes VOCs and CO present in the emissions. After reaction, emissionsthen flow into a combustion chamber and are held for a predeterminedperiod of time, after which the purified emissions flow through a secondset of components comprising a catalyst and a regenerative bed, andthence through an open outlet valve for venting to atmosphere or otheruse.

The regenerative bed comprises a honeycombed heat media, and thecatalytic bed comprises a plurality of particles, generally spherical inshape and uniform in size. However, depending on design considerations,the catalytic bed may also contain catalytic saddles or honeycombedstructured catalysts. A grate or honeycombed structure is disposedbetween the catalyst and the combustion chamber, with passages smallenough in both the regenerative bed and in the grate to inhibit lateralflow of catalyst out of the catalyst chamber.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic representation of a horizontal regenerativecatalytic oxidizer unit, in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

In accordance with the present invention, a first embodiment for ahorizontal regenerative catalytic oxidizer (hereinafter "RC0") 10, isshown in FIG. 1 comprising two distribution/collection plenums, 14 and16, and two conventional regenerator chambers 18 and 20. Heatregenerative chambers 18 and 20 are provided with a conventionalhoneycombed heat exchange media preferably having a specific heat of0.21 BTU/lb/°F., a density of at least 40 lb/ft³, and a geometric areaof 200 ft² /ft³, to provide maximum thermal efficiency.

The RCO 10 further comprises catalytic chambers 22 and 24 preferablyspherical in shape and 0.25 to 1 inch in diameter, and having a crushstrength of greater than 40 psi. The catalytic chambers may alsocomprise saddles or other random particles if cleaning or regenerationis a design criterion. If cleaning is not critical, then honeycombedcatalysts may be used.

The catalytic chambers 22 and 24 have upper access chutes 26 and 28,controlled by valves 34 and 36, and lower discharge chutes 38 and 40controlled by valves 42 and 44, respectively. The chutes 26, 28, 38, and40 provide for replacement and removal of catalyst as well as forregeneration thereof by rinsing the top of the chamber down and thendraining from the bottom chute.

Suitable grates or honeycomb structures 45 and 46, having passagewaystwo thirds, or less the size of the diameter of the average catalyticparticle, and immediately following and communicating with catalyticchambers 22 and 24, respectively, are used to inhibit migration of thecatalyst out of the catalytic chambers. Catalytic particles aretherefore trapped within the catalytic chambers 22 and 24 formed betweenthe honeycombed heat exchange media 18 and 20, and the grates 45 and 46,respectively.

A common combustion chamber 47 communicates with each catalytic bed 22and 24. Fuel, for example natural gas, is supplied to the combustionchamber 47 from a fuel controller and burner 48 or other heat source.Contaminated emission feed duct 50 admits process emissions into the RCO10 through a pair of inlet ducts 52 and 54. Cleansed air is conductedaway from the RCO 10 by a pair of outlet ducts 56 and 58, which feed acleansed exhaust duct 60, and is vented to atmosphere. The RCO 10utilizes a plurality of valves 62, 64, 66, and 68 to control the cyclicflow of contaminated emissions and cleansed air to and from the RCO.

The flow control valves 62, 64, 66, and 68 are preferably power actuatedelectronically controlled valves of the type disclosed in U.S. Pat. No.5,000,422, or copending U.S. application Ser. No. 08/087,658, filedJul., 6, 1993, entitled, "Air Seal Valve" now U.S. Pat. No. 5,327,928.Power actuation of the valves 62, 64, 66, and 68 under the control of acomputer offers precise timing and positive actuation.

In a first operational cycle, inlet valve 62 is open, while inlet valve66 is closed, thereby establishing chamber 18 as a feed bed and chamber20 as an exhaust bed. Contaminated emissions, i.e. industrial processexhaust, flow through feed duct 50, inlet valve 62, inlet duct 52 anddistribution/ collection plenum 14, to regenerative chamber 18 whereinthe emissions are preheated. The emissions then flow through catalyst22, where heat produced by burner 48 causes the catalyst tocatalytically effect oxidation of a substantial concentration of VOCsand CO at temperatures typically below 800° F. (≈466° C.). The catalyst22 may directly communicate with bed 18 (as shown), or alternatively,may be physically separated while in the same housing.

In accordance with the present invention, the oxidized emissions thenflow through common combustion chamber 47. The emissions are elevated tothe temperature of chamber 47 for a retention time of, for example,about 0.5 seconds. The combustion chamber 47 enhances efficiency of theRCO by insuring VOC and Co destruction.

The cleansed exhaust then flows out of the combustion chamber 47 intocatalyst 24, through regenerative chamber 20, distribution/collectionplenum 16, outlet duct 58, and open outlet valve 68 to the cleansedexhaust duct 60 for discharge to the atmosphere or other use. Efficiencyof the RCO 10 is further enhanced because any residual amounts of VOCsand CO which escape combustion are oxidized by the catalyst 24. Sinceregenerative chamber 20 is operating as the exhaust bed, a heat exchangebetween the hot exhaust and the bed media preheats the bed, therebyestablishing the desired regenerative effect as outlet flow continuesthrough open outlet valve 58 from bed 20.

Computer automated control is used to facilitate a change in cycles.Outlet valve 68 begins to close while outlet valve 64 begins to open.Simultaneously, inlet valve 66 begins to open as inlet valve 62 beginsto close. Ultimately, the second abatement cycle begins with inlet valve66 open, outlet valve 64 open, inlet valve 62 closed, and outlet valve68 closed.

In operation, the second leg of the abatement cycle flows in reverseorder with respect to the first cycle but with similar features. Thus,contaminated emissions flow from feed duct 50. through open inlet valve66, inlet duct 54, and distribution/collection plenum 16 to regenerativechamber 20, now operating as the feed bed. The catalyst 24 oxidizes VOCsand CO in the emissions. The emissions then flow through commoncombustion chamber 47, thence outwardly through catalyst 22, regenerator18, distribution/collection plenum l4, outlet duct 56, valve 64, andexhaust duct 60. The cycles switch again, as described hereinabove,thereby facilitating alternate flow of the process gases.

The horizontal configuration allows for easy access and simplifiedmaintenance when removing and replacing the catalyst, or when cleaningor regenerating the catalyst by introducing water or cleaning solvents,for example, through the upper chute. Unlike the vertical configuration,any solids that are rinsed from the catalyst will settle or drain to thelower chute, as opposed to the heat media bed, and can be emptied therealong with the contaminated fluid.

Finally, the horizontal configuration provides for a reduced volume orsize of the RCO per cubic foot of process emissions processed, andtherefore a reduction in raw materials required when manufacturing theRCO. The smaller footprint provides greater efficiency per cubic foot ofthe RCO, as compared to the vertical configuration.

While FIG. 1 illustrates the present invention as applied to tworegenerative bed systems, one of ordinary skill in the art will readilyappreciate that the features and advantages of the present invention areequally applicable to other numbers of regenerative beds, for example athree or a four bed RCO. A purge cycle, for example, as taught in U.S.Pat. No. 5,163,829 to Wildenberg, the discussion of which is herebyincorporated by reference, may also be incorporated. Furthermore, thisinvention may also accommodate other purification means such as aselective catalytic reduction bed disclosed in coowned and copendingapplication Ser. No. 08,280,944, filed Jul. 27, 1994, and entitled,"Integrated Regenerative Catalytic Oxidation/Selective CatalyticReduction Abatement System"now U.S. Pat No. 5,589,142, designed toreduce NOX emissions to N₂.

While the preferred embodiment of the invention has been disclosed, itshould be appreciated that the invention is susceptible of modificationwithout departing from the scope of the following claims.

We claim:
 1. A regenerative catalytic oxidizer for removal ofcontaminants from process emissions comprising:an input regenerativeunit having means on one side thereof for receiving a horizontal flow ofcontaminated process emissions; an exhaust regenerative unit havingmeans on one side thereof for receiving a horizontal flow of hotcleansed exhaust; a combustion chamber connected between andhorizontally configured with said input regenerative unit and saidexhaust regenerative unit for heating said process emissions to anabatement temperature sufficient to destroy said contaminants; a firstcatalytic oxidizer connected between and horizontally configured withsaid input regenerative unit and said combustion chamber, said firstcatalytic oxidizer comprising an upper and lower access chute, saidupper access chute having a first valve and said lower access chutehaving a second valve; a first catalyst containment structure connectedbetween and horizontally configured with said first catalytic oxidizerand said combustion chamber; a second catalytic oxidizer connectedbetween and horizontally configured with said exhaust regenerative unitand said combustion chamber, said second catalytic oxidizer comprisingan upper and lower access chute, said upper access chute having a firstvalve and said lower access chute having a second valve; a secondcatalyst containment structure connected between and horizontallyconfigured with said second catalytic oxidizer and said combustionchamber; wherein said catalytic oxidizers comprise catalytic media, andsaid catalyst containment structures comprise emission passages of asize small enough to inhibit lateral flow of said catalytic media, andmeans for controlling the input of said process emissions and theremoval of said cleansed exhaust thereby controlling the heat exchangein said regenerative units; wherein said means periodically reverse thedirection of flow of said process emissions such that said inputregenerative unit and said exhaust regenerative unit are alternated sothat said exhaust regenerative unit operates as the input regenerativeunit and said input regenerative unit operates as the exhaustregenerative unit.
 2. A regenerative catalytic oxidizer of claim 1wherein said input regenerative unit and said exhaust regenerative uniteach comprise honeycombed heat exchange media.
 3. A regenerativecatalytic oxidizer of claim 1 wherein said catalytic media comprises aplurality of catalyst particles.